University of Washington researchers found a 15 percent lower risk of prostate cancer in men who'd been circumcised before they first had intercourse compared to men who hadn't been.

How could that be? There's evidence, the researchers write, that some cancers are caused by infections. Take, for instance, human papillomavirus and cancers of the cervix and throat, where the link is pretty direct.

But in other cases, such as prostate cancer, the mechanism, if there is one, is a bit more convoluted. An infection, such as prostatitis, can lead to inflammation of the prostate. The body's response may damage DNA and contribute to the development of some cancers.

So prevent an infection and you might reduce the risk. When it comes to HIV and HPV, for instance, there's quite a bit of evidence that circumcision can reduce the risk of infection.

But the difference in circumcision status between the groups in the latest studies wasn't huge — only about four percentage points. Around 65 percent of the men in the cancer group had been circumcised before their first intercourse versus 69 percent in the comparison group.

The researchers were circumspect about circumcision as cancer protection. "I would not go out and advocate for widespread circumcision to prevent prostate cancer," Jonathan Wright, a urologist at the University of Washington med school author of the study, told Reuters Health. "We see an association, but it doesn't prove causality."